Modus operandi, often abbreviated m.o. or MO, is Latin for way of working. In English, the loanword is usually used to refer to a way in which someone routinely does something, but it can also be used more generally to refer to mode of operation.
The word is well established in English—the earliest examples are from the 17th century—so there is no need to italicize it in normal use.
The modus operandi, which persists even now, was to buy a company or business mostly with debt and then charge that company a ”transaction fee”. [Sydney Morning Herald]
Needless to say, Walker’s opponents describe his m.o. differently. [Boston Globe]
The targeted killings of former Mujahedeen commanders in the north and tribal elders in the south mark a strategic shift in the Taliban’s modus operandi. [New York Times]
Those familiar with EU modus operandi suggested that particular move was unlikely to cut much ice in Brussels. [Irish Times]
Their M.O. was to target Hispanic-owned businesses, create a diversion and then swipe a money bag or register receipts. [Cliffview Pilot]